review of git physiology

Review of GIT Physiology

Prof.Dr.Rashid Mahmood

© Prof.Dr.Rashid Mahmod 2

GIT: A long tube with Accessory glands


Lesson ContentsMouth EsophagusStomachPyloric SphincterSmall intestineIleo-Cecal Valve & SphincterLarge intestineInternal & External Anal SphincterAccessory glands


MouthIngestion of food

MasticationSwallowing

3 Stages i. Voluntary Stage (Movement of Tongue)ii. Pharyngeal Stage (Involuntary) (Swallowing

Reflex)iii. Esophageal Stage (Involuntary)

Khyber Girls Medical College Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood

5

Mastication (Chewing Reflex)• Components of reflex

1. Stimulus2. Receptors3. Afferent Nerve4. CNS5. Efferent Nerve6. Effector7. Response

• Components of Chewing reflex1. Bolus of Food2. Receptors of Sensory Nerves3. 5th Nerve4. Swallowing Centre5. 5th Nerve6. Muscles of Mastication7. Reflex Inhibition →Rebound Contraction (Stretch Reflex)

Khyber Girls Medical College Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood Prof.Dr.Rashid Mahmood

6Swallowing

Oropharyngeal stage of swallowing

Resting


Swallowing (Deglutition) Reflex

1. Stimulus→ Touch2. Receptors→ Tactile3. Afferent Nerve→ 5,94. CNS→ Swallowing Centre (Medulla &

Lower Pons)5. Efferent Nerve→ 5,9,10,126. Effector→ Muscles of Pharynx & Upper

esophagus7. Response → Contraction


Esophagus3rd Stage of swallowing No secretion except mucus, more

marked at upper & lower end PeristalsisUpper and lower esophageal Sphincter


StomachMovements (Motor functions)Secretions Digestion AbsorptionRegulation


Movements (Motor functions) of Stomach

1. Storage• Until food is processed in stomach and intestine

2. Mixing (with gastric secretions)• Unless semifluid mixture: chyme

3. Slow emptying• At a rate suitable for digestion and absorption

in small intestine4. Hunger contractions


Secretions of Stomach

Components1. HCl2. Pepsins3. Gastric Lipase 4. Gastric Amylase5. Mucus6. Intrinsic factor7. Gelatinase

(Liquefies Gelatin)8. Electrolytes9. Water

Phases Cephalic

PhaseGastric PhaseIntestinal

Phase


Digestion in Stomach1. Gastric Lipase (Digestion of lipids)2. Gastric Amylase (Digestion of

carbohydrates)3.Pepsinogen (Digestion of Proteins)

Pepsinogen

Pepsin

HClCauses proteolysis


Absorption in Stomach Water, if the body is dehydrated. Medication, like aspirin. Amino acids.


Regulation of Gastric Functions

Nervous Control Enteric Nervous System Autonomic Nervous System Reflexes:

Entero Gastric Reflex Cephalic Phase of Gastric Secretion

Hormonal Control Gastrin Secretin CCK GIP Motilin


Pyloric SphincterPyloric Pump & Gastric Emptying

1. Gastric factors (Excitatory)

Hormonal control GASTRIN →

Mild to moderate stimulation of gastric movements

Nervous control local Myenteric

reflexes

2. Duodenal factors (Inhibitory)(more powerful)

Nervous control Enterogastric nervous

reflexes Hormonal control

i. Cholecystokinin ii. Secretiniii. GIP


Small IntestineMovementsSecretions Digestion AbsorptionRegulation


Movements of Small Intestine1. Mixing (Segmentation Contractions)2. Propulsive (Peristalsis)

Overlap

3. Movements of Muscularis MucosaFolds

↑ surface area4. Contraction of villi

“milk” the villi↑ lymph flow


Secretion of Small IntestineSecreted Into Intestinal Lumen

EnterokinaseEnterocytes covering the villi contain enzymes

Digestion during absorptionFor digestion of proteins

PeptidasesFor digestion of carbohydrates

Sucrase, maltase, isomaltase, lactaseFor digestion of fats

Intestinal lipase

Hormones Secreted by Small Intestine:

SecretinCCKMotilin


Digestion in Small IntestineFinal Digestion occurs inside the

Enterocytes lining the epithelium of small intestine.

Digestion of Carbohydrates

Cellulose: Not digested

Action of Ptylin (Amylase):5% digestion in mouth

15-35% in stomach (before it is inactivated by HCl)

More Powerful

Contd………

Absorbed

Digestion of Proteins

Collagen (Meat)

Digestion of Fats

Lingual Lipase: < 10% digestion (Not important)Enteric Lipase: < 10% digestion (Not important)

Cholesterol Esterase digests Cholesterol Esters

Phospolipase A2 digests Phospolipids

Which is the main enzyme for digestion of fats?


Absorption in Small IntestineFinal Absorption of all nutrients by

enterocytes

Absorption of Carbohydrates

A small fraction as Disaccharides Mainly Monosaccharides

Glucose (80%) Galactose

Sodium Co-Transport Fructose

Facilitated Diffusion Presence of glucose also facilitates reabsorption of Sodium

Absorption of Proteins

Protein molecules : rarely absorbed → antigenic reaction Absorbed as

Tripeptides Bipeptides Amino Acids

Mainly Co-transport with Sodium

Absorption of Fats

Fats

Monoglycerides

Fatty Acids

Bile Micelles

Microvilli

Bile Acids Monoglycerides

Fatty Acids

Bile Acids

Epithelial Cells

New Triglycerides

Chylomicrons

Lymph

Intestinal Lumen

++ +

+


Regulation of Functions of Small Intestine

Nervous ControlEnteric Nervous SystemAutonomic Nervous SystemReflexes

Gastro-EntericGastro-Ileal etc

Hormonal ControlSecretin CCK

Ileocecal valve andIleocecal sphincter

Excitatory factors

Inhibitory factors


Large IntestineMovements SecretionsNo DigestionAbsorptionFormation of FecesOther Functions

Movements of Colon

Mixing Movements (Haustrations) Proximal half

Propulsive Movements (Mass Movements) Distal half

Functions of colon: Absorption Storage of fecal matter

Secretions of Large Intestine:Mucus secretion

Crypts of Lieberkϋhan No villi No enzymes Moderate amount of bicarbonate ions

Absorption in Large Intestine

Proximal Half: Absorbing Colon

Water Electrolytes

Distal Half: Storage Colon

Formation of Feces No villi

Other Functions of Large Intestine

Bacteria Normally present Substances formed as a result of bacterial action:

Vitamin K Vitamin B12 Thiamine Riboflavin Gases (flatus)

CO2

Methane Hydrogen

External & Internal Anal Sphincter:Defecation reflex

Defecation Reflexes

Intrinsic Reflex Parasympathetic Defection reflex

11Prof .Dr. Rashid Mahmood

Defecation

• Rectum is empty most of the time– Weak functional sphincter at juncture between

sigmoid colon & rectum– Sharp angulation

• Feces into rectum → Defecation reflex– Desire for Defecation– Reflex contraction of rectum– Reflex relaxation of anal sphincters

Voluntary/conscious/subconscious involuntary

External Internal Pudendal nerve


Accessory glandsSalivary GlandsPancreasLiver/ Gall Bladder


Salivary Glands: Saliva

1. Digestion i. Salivary Amylase

Secreted by salivary glandsii. Lingual lipase

Secreted by glands on the tongue

2. Articulation3. Moistening of food4. Mastication 5. Water regulation (thirst)6. Taste receptors7. Swallowing 8. Keeps mouth clean9. Neutralization of gastric

acid Relieve of heartburn

10. Protection from bacteriai. Wash away bacteriaii. Wash away the food of

bacteriaiii. Destroy bacteria

11. Tooth Protection1. By neutralizing acid2. By affecting mineral

dissociation equilibrium by means of its calcium phosphate content.

3. Proline-rich proteins protect the tooth enamel and bind toxic tannins

12. Excretion:Urea, Heavy Metals, Drugs etc

PancreasComponents of Pancreatic Secretion1. Exocrine

i. Digestive enzymes Secreted by acinar cells

ii. HCO3- - Secreted by duct cells

2. Endocrinei. Insulinii. Glucagon

Functions of Liver

1. Formation and secretion of bile2. Nutrient and vitamin metabolism3. Inactivation of various substances4. Synthesis of plasma proteins5. Immunity

Functions of Bile

Digestion of fats Emulsification

Large fat particles →small fat particles Absorption of fats Excretion

Bilirubin End product of hemoglobin destruction

Excess cholesterol

Emptying of Gall Bladder

Food in DuodenumMainly Fatty Food

Cholecystokinin

BLOOD

GALL BLADDER

EMPTYING

RELAXATION OF SPHINCTER OF ODDI

duodenum

Vagus nerve

Food in mouth

The EndQuestions? Next:

EOME

review of git physiology

Health & Medicine